This refers to the traditional calendar of the Tibetan nationality. According to historical records, Tibetan people had developed their own calendar before 100 BC, calculating the date according to the movement of the moon. Several hundred years later, Bon religion believers couId calculate the precise time of the winter solstice, regarding it as the starting point of a new year. Various festivals and rituals were formed on that basis. In the 7th century, Princess Wencheng and Princess Jincheng of the Tang Dynasty who married kings of Tibet took the mainland calendar with them to the region. From that time, the ancient Tibetan calendar, Chinese calendar and the Indian calendar were combined. In the Yuan Dynasty, the unique calendar integrating the “Ten Heavenly Stems, Earthly Branches and Five elements”, was formed. The existing Tibetan almanac first appeared in the 13th century (the Yuan Dynasty). In the 19th century the Tibetan almanac had become increasingly perfect.
The Tibetan calendar is based on alternating yin and yang and a year consists of 354 days. "The yin (third of the Twelve Earthly Branches) month is regarded as the first month of the new year. The month is based on the movement cycle of the moon. “Dayue” or Big Month, consisting of 30 days, and “Xiaoyue” or Small Month, consisting of 29 days alternate. One leap month is used to adjust the relationship between months and seasons.
According to the capricious climate of the plateau, the Tibetan calendar formed a unique way of dividing a year into six seasons, namely spring, late spring, summer, autumn, winter and late winter. This division conforms to the climatic characteristics of most areas on the Qinghai-Tibet Plateau. Generally speaking, the longest season in Tibet is winter, followed by spring, autumn and summer in succession. In some alpine areas, the climate in summer, spring and autumn is almost the same. All kinds of solar terms and phenological phenomena in the Tibetan calendar not only reflect climate changes all year round, and all kinds of natural celestial phenomena, but also predict the climate changes over a long period. This is a major feature of the calendrical system.